1. Field of the Invention
The present invention relates to high-frequency modules including a transmission circuit and a reception circuit connected to an antenna.
2. Description of the Related Art
Various high-frequency modules have been proposed that include a transmission circuit and a reception circuit connected to an antenna or a plurality of transmission/reception circuits connected to the antenna. In such high-frequency modules, two circuits (hereinafter, referred to as a transmission circuit and a reception circuit for ease of explanation) are connected to an antenna through a duplexer or an integrated circuit (IC) switch. The duplexer includes a common terminal to be connected to the antenna, and individual terminals to be connected to the respective transmission and reception circuits. The duplexer also includes, for example, a first surface acoustic wave (SAW) filter having a passband in a transmission signal band, and a second SAW filter having a passband in a reception signal band. The first SAW filter is arranged between the transmission-side individual terminal and the common terminal, and the second SAW filter is arranged between the reception-side individual terminal and the common terminal.
Furthermore, in such high-frequency modules, a matching circuit arranged to match impedance between the duplexer and an external circuit, such as the antenna connected to the common terminal, is connected to the common terminal.
As described in Japanese Unexamined Patent Application Publication No. 2003-163570, a high-frequency module is defined by a multilayer circuit module. In the high-frequency module, the duplexer is a discrete circuit element and is mounted on a multilayer substrate defining the multilayer circuit module. Additionally, the matching circuit defined by an electrode pattern disposed in the multilayer substrate or on a surface of the substrate. The duplexer and the matching circuit are connected to a common ground electrode arranged near the duplexer and the matching circuit.
However, the configuration described above may cause the following problems. FIGS. 5A and 5B are cross-sectional views to describe the problems caused in a high-frequency module according to the related art that includes a configuration described in Japanese Unexamined Patent Application Publication No. 2003-163570.
In a high-frequency module 1H shown in FIG. 5A, a wiring pattern 22H arranged near a common terminal of a duplexer 101 and a wiring pattern 21H arranged near individual terminals of the duplexer 101 are closely arranged in the same layer. Accordingly, the wiring pattern 21H is electromagnetically coupled to the wiring pattern 22H. Because of this electromagnetic coupling, a signal originally flowing from the common terminal of the duplexer 101 to a matching element 102 leaks to the individual terminals of the duplexer 101 through the wiring patterns 22H and 21H. Since a common ground 11H closely opposes to the wiring pattern 21H, the common ground 11H is electromagnetically coupled to the wiring pattern 21H. Because of this electromagnetic coupling, a signal originally flowing from the common terminal of the duplexer 101 to ground through the matching element 102 leaks to the individual terminals of the duplexer 101 through the common ground 11H and the wiring pattern 21H.
In a high-frequency module 1H shown in FIG. 5B, since a wiring pattern 22H′ arranged near a common terminal of a duplexer 101 and a wiring pattern 21H arranged near individual terminals of the duplexer 101 are arranged so as to be separated from each other in a lamination direction through a common ground 11H, electromagnetic coupling in the same layer is prevented. However, electromagnetic coupling between the common ground 11H and the wiring pattern 21H illustrated in FIG. 5A occurs. Furthermore, referring to FIG. 5B, since the common ground 11H closely opposes to the wiring pattern 22H′, the common ground 11H is electromagnetically coupled to the wiring pattern 22H′. Because of this electromagnetic coupling, a signal originally flowing from the common terminal of the duplexer 101 to the matching element 102 leaks to the individual terminals of the duplexer 101 through the wiring pattern 22H′, the common ground 11H, and the wiring pattern 21H.
Since, for example, a transmission signal that is input from the transmission-side individual terminal of the duplexer 101 and output to the common terminal thereof leaks to a reception circuit in the configurations according to the related art, isolation between a transmission circuit and the reception circuit is reduced in a high-frequency module even if the duplexer 101 provides the desired isolation between the individual terminals.